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This article will go through the different factors to consider when buying a projector and what the best lumens are for your needs. We’ll also discuss how to calculate lumens for your specific needs.

## What are Lumens?

Lumens measure the amount of light coming out of a surface, not how bright something is in general. For example, if you hold a candle 20 inches from your face, you might say it’s bright but it doesn’t have many lumens because there aren’t many candles that far away from each other – they just don’t cast much light. The same applies to projectors, because we aren’t looking for something that will be the brightest thing in the room. We are only looking for a certain type of brightness when we say lumens, so don’t go comparing a projector to the sun. 🙂

**Read more: Best Portable Projectors in India 2021: Expert’s Choice**

## Calculating Lumens in your Room

The easiest way is by just doing a little math to calculate how many lumens you need based on your application. For example, if you are going to use it in a small room and place it 10′ away from a screen and you want 150″ screen image (which is very common), then you will need about 280 lumens per square foot in that room. Make sure to remember that this is general, and it will depend on your screen size, room size and lumens per square foot of the projector.

If you are planning to use it in a really big room, then you may want to consider using an RGBRGB color wheel instead of RGBCMY color wheel in your projector.

When looking at lumens of the projector’s literature, the minimum lumen output is going to be with all the lights off (0 lumens). This is what you will get when the colors are pure red/green/blue and no color wheel is present.

If you are looking for a higher lumen output (for example, you want to use a projector in a well lit room), then look for projectors with 6-chip RGBRGB color wheels. They put out roughly double the number of lumens.

The six-color wheel projectors also have three color wheels inside, so they are more expensive than the RGBRGB projectors. If you are looking at a 6-chip projector, double check to make sure it has an RGBCMY color wheel setup because RGBRGBs will produce blurry images. 6-chip RGBRGB projectors are more expensive but have longer lamp life, so it’s all about what you need.

The Interpreter Projector has RGBRGB color wheels and more lumens at the same cost as an equivalent 6-chip RGBRGB projector.

**Read here: Best Projector under 10000 Rupees in India 2021**

## Calculating Lumens for Screen Size

To calculate lumens for a specific screen size, you just need to find out how many square inches there are in that screen size, then multiply by the product of number of colors per pixel (usually 1 or 2) and lumen value of each color.

For example, let’s say you want to calculate for a 100″ image and the pixel count is 1080p (2 colors per pixel). First, you want to take the diagonal measurement of the image (100 inches) and then multiple it by 1.78 because there are 1.78 steradians in a circle.

Then calculate lumen value with this formula:

Lumens = 2 * π * LampsPerPixel * 0.999

Next, multiply lumens by 100 because you are looking for lumens per square foot of the room, then multiply by 100 again to get it in foot-Lamberts so that we can use it with our previous equation.

Lumens for a 100″ Screen = 2 * π * LampsPerPixel * 0.999 * 100 = 111,200 lumen

Then we divide by the number of square inches in a meter2:

Lumens per square foot = Lumens / (m2)

**Relevant reading: What Is Projector Throw Ratio And Why Is My Projector Dim?**

You do this calculation based on your screen size. To calculate lumens for a 500″ image, you would just take the 500 inches step down from the diagonal size and multiply by 1.78:

500″ Image Diagonal = 500″ / 1.78 * 1.8 = 296.06 square inches, so we take the lumen value of 111,200 and divide by 296.06:

Lumens per square foot = 111,200 / 296.06 = 365.38 lumens per square foot

Let’s say you decide to go with a screen that is a little smaller than that, so you want a 200″ image instead. You just take 200 inches and step it down by 1.78 (200 / 1.78 * 1.8) to get 138 square inches:

138″ Image Diagonal = 138″ / 1.78 * 1.8 = 77.98 square inches, so we take the lumens value of 111,200 and divide by 77.98:

Lumens per square foot = 111,200 / 77.98 = 206.24 lumens per square foot

Let’s say you decide on a screen size that is double your diagonal (300″), but you don’t want it to be as bright as the 200″ screen above. You just multiply 1.78 for every 3″ of diagonal by 2 for every 1 lumen more you would like to have than the 200″. So 300″ / 1.78 * 2 * 1 * 2 = 132:

300″ Image Diagonal = 300/1.78 * 1.8 * 2 = 132 square inches, so we take the lumens value of 111,200 and divide by 132:

Lumens per square foot = 111,200 / 132 = 95.41 lumens per square foot

*Note that this only works for a 200″ screen because something with a 300″ diagonal is 4 times larger than the 200″ screen projection area. So if you are trying to figure out how many lumens for a 400″ screen, you would have to multiply 1.8 by 4 or just multiply 1.78 by 4:

400″ Image Diagonal = 400/1.78 * 2 * 1 * 2 = 212.5 square inches, so we take the lumens value of 111,200 and divide by 212.5:

Lumens per square foot = 111,200 / 212.5 = 77.96 lumens per square foot

**Also read: Best 4k Projectors in India 2021**

## Calculating Lumens for Color Wheel Size

To calculate lumens for a color wheel that has fewer colors than the projector’s factory installed RGBRGB color wheel, you just do a little math to find out how many square inches there are in that screen size and multiply by the product of number of colors per pixel (usually 1 or 2) multiplied by lumen value of each color.

For example, let’s say you want to calculate for a color wheel that has only 2 colors per pixel (which is common with less expensive projectors). First, you want to take the diagonal measurement of the image and divide it by 2.72 so that we can use a square-cube law, which gives us the same angles in all related percentages.

Then calculate lumen value with this formula:

Lumens = π * LampsPerPixel * 0.999

Next, multiply lumens by 100 to get it in foot-Lamberts so that we can use it with our previous equation.

Lumens for a 100″ Screen = π * LampsPerPixel * 0.999 / 2 = 2 * π * LampsPerPixel * 0.999 = 3.142 lumens

Then we divide by the number of square inches in a meter2:

Lumens per square foot = Lumens / (m2)

You do this calculation based on your screen size. To calculate lumens for a 500″ image, you would just take the 500 inches step down from the diagonal size and divide by 2.72:

500″ Image Diagonal = 500/ 2.72 * 1.8 = 180.59 square inches, so we take the lumen value of 3.142 and divide by 180.59:

Lumens per square foot = 3.142 / 180.59 = 16 lumens per square foot

*Note that this only works for a 200″ screen because something with a 300″ diagonal is 4 times larger than the 200″ screen projection area. So if you are trying to figure out how many lumens for a 400″ screen, you would have to divide by 2 again:

400″ Image Diagonal = 400/ 2 * 1.78 * 1 * 1 = 88.75 square inches, so we take the lumen value of 3.142 and divide by 88.75:

Lumens per square foot = 3.142 / 88.75 = 29.64 lumens per square foot

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## Calculating Lumens for Projector Size

To calculate lumens for a projector that has more than one color wheel, you just need to know how many colors are in each color wheel, which is expected to be 6 or 8 or more since there are usually two RGs and two Gs, one blue and one green in each color wheel. So you can do the calculation as shown above for each color wheel.

Let’s say you just wanted to know how many lumens for two color wheels (6 colors in each color wheel or 8 colors in each color wheel). You just take the number of square inches in your screen size and divide by 2.72:

200″ Image Diagonal = 200/ 2.72 * 1.8 = 77 square inches, so we take the lumens value of 3.142 and divide by 77:

Lumens per square foot = 3.142 / 77 = 30.8 lumens per square foot

*For a 400″ image diagonal, you would just divide by 2 again, so you would have to calculate it like this:

400″ Image Diagonal = 400 / 2 * 1.78 * 1 * 1 = 88.75 square inches, so we take the lumen value of 3.142 and divide by 88.75:

Lumens per square foot = 3.142 / 88.75 = 29.64 lumens per square foot

Lumens for an XGA 1.0 (Also Called WUXGA) Projector

This is the very common resolution of a 1280×1024 pixel projector. You will find this size on most recently manufactured projectors that look pretty nice and have improved image quality. It is simply a format upgrade from the VGA standard and it is much better than VGA in every way, but it still isn’t a great display for all applications. The biggest problem with XGA projectors is that they have very limited persistence and dimming capabilities so you need to either make your image brighter or dim it less to get the same effect as a regular DLP projector.

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